Prof. Tyndall on the Conformation of the Alps. 259 



trace of fissure. An example of this kind occurs near the 

 Bernina Gasthaus, about two hours from Pontresina. A little 

 way below the junction of the two streams from the Bernina 

 Pass and the Heuthal the river flows through a channel cut 

 by itself, and 20 or 30 feet in depth. At some places the river- 

 bed is covered with rolled stones ; at other places it is bare, but 

 shows no trace of fissure. The abstract power of water (if I may 

 use the term) to cut through rock is demonstrated by such in- 

 stances. But if water is competent to form a gorge without the 

 aid of a fissure, why assume the existence of such in cases like 

 that at Pontresina ? It seems far more philosophical to accept 

 the simple and impressive history written on the walls of those 

 gorges by the agent which produced them. 



Numerous cases might be pointed out, varying in mag- 

 nitude, but all identical in kind, of barriers which crossed 

 valleys and formed lakes having been cut through by rivers, 

 narrow gorges being the consequence. One of the most famous 

 examples of this kind is the Finsteraarschlucht in the Valley of 

 Hasli. Here the ridge called the Kirchet seems split across, and 

 the river Aar rushes through the fissure. Behind the barrier 

 we have the meadows and pastures of Imhof resting on the sedi- 

 ment of an ancient lake. Were this an isolated case, one might 

 reasonably conclude that the Finsteraarschlucht was produced by 

 an earthquake, as some suppose it to have been ; but when we 

 find it to be a single sample of actions which are frequent in the 

 Alps — when probably a hundred cases of the same kind, though 

 different in magnitude, can be pointed out — it seems quite un- 

 philosophical to assume that in each particular case an earthquake 

 was at hand to form a channel for the river. As in the case of 

 the barrier at Pontresina, the Kirchet, after the retreat of the 

 Aar glacier, dammed the waters flowing from it, thus forming a 

 lake, on the bed of which now stands the village of Imhof. Over 

 this barrier the Aar tumbled towards Meyringen, cutting, as 

 the centuries passed, its bed ever deeper, until finally it became 

 deep enough to drain the lake, leaving in its place the alluvial 

 plain through which the river now flows in a definite channel. 



But it may be urged that it is not necessary to assume the 

 operation of a special earthquake to split each particular barrier. 

 The broad view taken by the advocates of the fracture theory is 

 that the valleys are the tracks of the fissures produced by the 

 upheaval of the land, and the cracks across the barriers to which 

 I have referred are in reality portions of the great cracks which 

 formed the valleys. Such an argument, however, would virtu- 

 ally concede the theory of erosion as applied to the valleys of the 

 Alps. These narrow channels, often not more than 20 or 30 feet 

 across, sometimes even narrower, frequently occur at the bottom 



